Browsing by Author "Jeno, Katherine"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    The effect of temperature on the development of encapsulated embryos of Concholepas concholepas along a latitudinal cline
    (2007) Fernandez, Miriam; Calderon, Ricardo; Cancino, Juan M.; Jeno, Katherine
    Encapsulating species face more constraints than active brooders in adjusting oxygen supply to the needs of the embryos. Therefore, the packing of embryos in gelatinous egg masses or egg capsules is expected to be adjusted to the temperature and oxygen conditions that the embryos are likely to experience . We studied the patterns of embryo packing (number of embryos per unit area) of the gastropod, Concholepas concholepas, from 14 sites over an extended geographic area spanning 220 of latitude off the coast of Chile. A clear break in the patterns of embryo packing was found at approximately 29 to 300 S. Capsules collected at the sites located north of this break exhibited significantly fewer embryos per unit area than capsules from southern sites. Embryo packing is correlated with mean temperature shortly before egg deposition. A set of laboratory experiments were conducted to determine if the effects of temperature reside in females (incubating females collected in 2 different sites at a common temperature) or in embryos (incubating capsules at different temperatures). Laboratory experiments showed that temperature does not affect the number of embryos that successfully develop in the capsules within the tolerated range of temperatures, but (toes influence developmental success at temperatures that are extreme for the sites of the sample population. Our results suggest that packing and protection of embryos in marine invertebrates might be linked to the capacity to supply oxygen to the brood, which can have important consequences for the distribution of brooding and encapsulating species across temperature gradients.
  • No Thumbnail Available
    Item
    The effects of temperature and oxygen availability on intracapsular development of Acanthina monodon (Gastropoda: Muricidae)
    (2006) Fernandez, Miriam; Pappalardo, Paula; Jeno, Katherine
    Freshwater and marine organisms show similar models of parental care and are faced with similar constraints to brood, which suggest that comparable environmental limits drive the evolution of parental care in aquatic systems. In fact, the low diffusion coefficient and solubility of oxygen in aquatic environments affect oxygen acquisition and therefore the capacity to aggregate embryos. The effect of other critical environmental variables, such as temperature, is less clear. We assessed the effects of temperature and oxygen availability on (1) the number of developed and undeveloped encapsulated embryos, (2) the proportion of embryos reaching advanced stages during intracapsular development (counting not only developed and undeveloped embryos but also abnormal embryos), (3) asynchrony in development (estimated only in capsules in which development occurred), and (4) final embryo size, as the first step toward identifying the main factors constraining parental care in the ocean. We used the gastropod Acanthina monodon as a model because it has an extended latitudinal range of distribution and exhibits feeding larvae during intracapsular development. The latter factor is relevant because previous studies have suggested that sibling cannibalism could be triggered by intracapsular competition for oxygen. Freshly laid egg capsules were collected and incubated until embryos hatched under different experimental temperatures (7, 11, 15 and 19 degrees C) and oxygen conditions (hypoxia: 50-60 % air saturation; normoxia; and hyperoxia: 150-160 %). More embryos remained in early stages at the end of the experimental period under hypoxia and at the highest experimental temperature. The mean number of developed embryos was significantly lower under hypoxia conditions than under normoxia and hyperoxia, but was not influenced by temperature. However, temperature negatively affected embryo size of developed embryos and the level of asynchrony (number of different developmental stages per capsule). This suggests that even when a comparable number of embryos develops at high temperature, subsequent survival may be affected, since developed embryos attained smaller sizes. The negative effect of high temperature on embryo aggregation has also been reported for Brachyuran crabs, affecting female patterns of oxygen provision and brooding costs. This evidence suggests that aggregating embryos in the ocean, even under optimum oxygen conditions, may be negatively affected at high temperatures. Spatial patterns of distribution of brooding species in the ocean tend to agree with this prediction. Our analysis is particularly relevant given the current increase in temperature and the proportion of anoxic areas in the world's oceans.